124 A. A. W. HUBRECHI. 
when once the basis has been established for an intimate 
relation along a considerable surface between the maternal 
blood-corpuscles circulating in the trophoblast and the 
embryonic ones also present in it. In this way, again, the 
placenta becomes established, the allantoic villi and their 
trophoblastic sheaths being spun out centripetally and not 
centrifugally. The massive dome-shaped placenta is thus in 
its full-grown condition, essentially again an embryonic 
structure in which maternal blood circulates (Hubr., ’94a, 
Figs. 11—15); the maternal epithelial proliferation has 
gradually been reduced to flat remnants in the region where 
the maternal blood enters the trophoblastic lacune. Also in 
Sorex the placenta is expelled as afterbirth, and the regene- 
ration of the mucosa comes about so quickly that young 
embryonic stages are often met with in a uterus which yet 
carries the unmistakable signs of the puerperium.! 
Tupaja is an example amongst Insectivores in which the 
disappearance of uterine glands in the region which will 
serve for the attachment of the placenta is not postponed till 
pregnancy has commenced and the formation of a maternal 
trophospongia has actually been inaugurated. Hven in the 
virginal uterus of Tupaja that region can already be dis- 
tinguished by the absence of glands. As 'lupaja has a double 
placenta, right and left of the developing embryo, which is 
always situated with its head turned towards the ostium 
uteri and with its belly facing the mesometrical attachment 
of the uterus, and as moreover Tupaja never produces 
neither more nor less than two young at a time (Hubrecht, 
°95, p, 10) these predisposed spots are situated very sym- 
metrically in the two uterine cornua. When pregnancy 
commences a general swelling of the uterine tissues is noted, 
1 One word may here be added concerning the mole’s placenta (see Vernhout 
(’94] and Strahl (790, 92]), which is not expelled as an after-birth, but which 
is resorbed in loco, embryonic trophoblastic tissue serving thus as a pabulum 
to maternal histolytic processes; the placenta, instead of deciduate, being 
thus, as I have termed it, contradeciduate, which term has been accepted 
by Hill (98, p. 424) for Perameles. 
